Cycloolefin copolymers have excellent moldability, dimensional stability, transparency and moisture barrier. However, the impact strength thereof is not sufficient and, therefore, improvement thereof has been conventionally investigated. It has been demanded to further improve the impact resistance with maintaining an excellent transparency that the cycloolefin copolymers possess.
It is generally known that alloying transparent brittle thermoplastic resins with incompatible rubber components enhances the impact resistance. This manner is also effective for cycloolefin copolymers. For example, a cycloolefin copolymer composition reinforced with commercially available block copolymers (such as SBS, SEBS and SIS) as a rubber component is disclosed in Japanese Patent Publication Kokai No. 1-256548.
In general, the impact resistance and the transparency of alloys of polymers incompatible with each other are greatly influenced by phase morphology of components constituting the polymer alloys.
Impact resistance of brittle thermoplastic resins cannot be always improved by merely alloying with rubber components. It is known that revelation of impact resistance is influenced by domain size of the rubber components dispersed in the continuous phase of the brittle thermoplastic resins, and the domain size appropriate for the revelation of impact resistance varies for every thermoplastic resin.
In many cases, the refractive indexes of a thermoplastic resin and a rubber component do not completely agree all over the visible ray band, so an excellent transparency that brittle thermoplastic resins possess is not always prevented from lowering by merely matching the refractive indexes of components constituting a polymer alloy. Therefore, the transparency of a polymer alloy is swayed by determination of the wave length at which the refractive indexes should be matched or determination of the domain size to be formed of the rubber component.
Objects of the present invention are to provide a cycloolefin copolymer resin composition having well-balanced impact resistance and transparency, and a process for preparing the composition